(1) Field of the Invention
The present invention relates to a variable displacement vane compressor including a rotor having a plurality of vanes and rotatably supported between a pair of side plates secured to opposite ends of a cylinder assembly in a housing so that a plurality of compression chambers are defined by the vanes in a space between the inner peripheral surface and the outer peripheral surface of the rotor, whereby the rotation of the rotor causes the compression chambers to be compressed and expanded and to be alternately connected to an inlet port and an outlet port to effect the suction, compression and discharge of refrigerant in the compression chambers, and a reciprocally rotatable displacement control plate located between the one of the side plates and the rotor to control the largest displacement of the compression chambers when closed.
(2) Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 61-76792 discloses a variable displacement vane compressor of the type mentioned above in which a spool chamber is provided at a position corresponding to the displacement control plate of one of the side plates to drive and control the displacement control plate. Accommodated in the spool chamber is a spool, which reciprocates in the spool chamber and which defines therein, a first pressure chamber into which the refrigerant having a pressure corresponding to the discharge pressure is introduced and a second pressure chamber into which an oil having a pressure corresponding to the discharge pressure is introduced, by a control valve mechanism actuated in response to the suction pressure. The spool is integrally connected to the displacement control plate by a pin and moves together therewith, to thereby drive and control the displacement control plate through the spool in accordance with the pressure balance between both pressure chambers. The control valve mechanism for controlling the introduction of the oil having a pressure corresponding to the discharge pressure into the second pressure chamber operates in response to the suction pressure, depending on the ambient temperature. Accordingly, the displacement control plate rotates about the axis of the rotor in accordance with the ambient temperature, to change the time at which, and the period for which, the fluid connection between the auxiliary inlet port formed in the displacement control plate and the compression chamber is established, so that a compression displacement depending on the ambient temperature can be obtained.
The time and the period of the connection of the auxiliary inlet port and the compression chamber are significant control parameters which ensure a desired compression displacement depending on the ambient temperature, but these control parameters are easily influenced by the efficiency of a sealing between the high pressure area and the low pressure area of the compressor. In particular, when refrigerant (gas) having a pressure corresponding to the discharge pressure is introduced into the first pressure chamber, a leakage of the high pressure gas may occur, to disturb the pressure balance between the first and second pressure chambers, so that the displacement control plate is moved in a direction in which the cooling power is reduced. This leakage of the high pressure gas from the first pressure chamber particularly depends on the efficiency of the sealing between the displacement control plate and the associated side plate, and thus a high sealing efficiency established between the high pressure area and the low pressure area is also required between the displacement control plate and the associated side plate. Nevertheless, it is very difficult to prevent a leakage of the high pressure gas by only the provision of a seal ring as used in most conventional compressors, and thus a reduced cooling efficiency depending on the ambient temperature occurs.
To solve the problem mentioned above, the assignee of the present application has proposed a vane compressor as shown in FIG. 6, in which an annular seal member 53 is provided between the displacement control plate 51 and the associated side plate 52 to isolate the high pressure area and the low pressure area, and the seal member 53 is connected to the oil feed passages 54 and 55 for introducing the oil having a pressure corresponding to the discharge pressure (Japanese Unexamined Patent Application No. 62-94867). In this arrangement, the seal member 53 ensures the isolation of the high pressure area from the low pressure area. The displacement control plate 51 is subject, on the front side thereof, (i.e., on the left side of FIG. 6), to the suction pressure P.sub.s which acts on the surface area A.sub.1 located outside the seal member 53, and the discharge pressure P.sub.4 which acts on the surface area A.sub.2, respectively. On the other hand, the displacement control plate 51 is subject, on the rear side thereof (i.e., on the right side in FIG. 6), to the pressure represented by (P.sub.s +P.sub.d)/2 from the cylinder, so that the displacement control plate 51 is pressed against the cylinder under a pressure (force) F represented by the following equation. ##EQU1##
Since the surface area A.sub.2 is not equal to the surface area (A.sub.3 /2), the pressure F is influenced by the discharge pressure P.sub.d, and a large discharge pressure increases the frictional force between the displacement control plate 51 and the cylinder, resulting in difficulties arising in the operation of the displacement control plate 51.
The primary object of the present invention is to eliminate the above-mentioned drawbacks of the prior art by providing a variable displacement vane compressor including a housing having therein a cylinder secured thereto, a pair of side plates secured to axially opposite ends of the cylinder, a rotor rotatably supported between the side plates and having a plurality of vanes movably supported in the rotor and coming into contact with the inner peripheral surface of the cylinder to define a plurality of compression chambers between the inner peripheral surface of the cylinder and the outer peripheral surface of the rotor, the volumes of the compression chambers being changed in accordance with the rotation of the rotor. The cylinder is provided with refrigerant inlet ports and refrigerant outlet ports which can be selectively connected to the compression chambers, and a reciprocally rotatable displacement control plate between the rotor and one of the side plates for controlling the largest displacement of the compression chambers when closed.
The improvement according to the present invention comprises a spool chamber provided in one side plate and opposed to the displacement control plate, a spool which reciprocates in the spool chamber to define a first pressure chamber into which a refrigerant having a pressure corresponding to the discharge pressure of the compressor is introduced and a second pressure chamber into which an oil having a pressure corresponding to the discharge pressure is introduced through a control valve in response to a suction pressure of the compressor, the spool and the displacement control plate being interconnected by a connecting member and moving together, an annular sealing means arranged between the displacement control plate and the one side plate for isolating a high pressure area from a low pressure area of the compressor, and a feed passage for introducing the oil having a pressure corresponding to the discharge pressure into the sealing means, the one side plate being provided with an elongated hole which permits movement of the connecting member extending therethrough, the annulus of the annular sealing means having a diameter smaller than that of a imaginary circle centered on the axis of rotation of the rotor and circumscribing the elongated hole, the annulus of the annular sealing means being eccentric to the axis of rotation of the rotor so that the elongated hole is included in the annulus of the annular sealing portion.
With this arrangement, the sealing efficiency between the displacement control plate and the associated side plate, which has an influence on the largest displacement when the compression chambers are closed, is increased by the introduction of the oil having a pressure corresponding to the discharge pressure, so that a leakage of the refrigerant gas having a pressure corresponding to the discharge pressure from the first pressure chamber can be effectively prevented. In addition, the pressing force which forces the displacement control plate onto the cylinder can be reduced, and as a result, the pressures in both pressure chambers can be properly balanced, using the suction pressure depending on the ambient temperature, and the displacement control plate can be smoothly operated, and thus a precise control of the largest displacement at the closure of the compression chambers in accordance with the ambient temperature can be realized.